View source for 2.5D

{{short description|Simulation of the appearance of being three-dimensional}}
{{Other uses|2.5D (disambiguation)}}
{{More citations needed|date=June 2023}}
{{Use mdy dates|date=October 2023}}
{{VG Graphics}}
'''2.5D''' (basic pronunciation '''two-and-a-half dimensional''') perspective refers to [[gameplay]] or movement in a [[video game]] or [[virtual reality]] environment that is restricted to a [[Plane (mathematics)|two-dimensional]] (2D) plane with little to no access to a [[Three-dimensional space|third dimension]] in a space that otherwise ''appears'' to be three-dimensional and is often simulated and rendered in a 3D digital environment.
This is similar but different from pseudo-3D perspective (sometimes called three-quarter view when the environment is portrayed from an angled top-down perspective), which refers to [[2D computer graphics|2D graphical projections]] and similar techniques used to cause images or scenes to simulate the appearance of being [[Three-dimensional space (mathematics)|three-dimensional]] (3D) when in fact they are not.
By contrast, games, spaces or perspectives that are simulated and rendered in 3D and used in 3D level design are said to be ''true 3D,'' and 2D rendered games made to appear as 2D without approximating a 3D image are said to be ''true 2D''.
Common in video games, 2.5D projections have also been useful in [[geographic visualization]] (GVIS) to help understand visual-cognitive spatial representations or 3D visualization.<ref name="MacEachren">[[Alan MacEachren|MacEachren, Alan]]. "GVIS Facilitating Visual Thinking."  In How Maps Work: Representation, Visualization, and Design, 355–458. New York: The Guilford Press, 1995.</ref>
The terms ''three-quarter perspective'' and ''three-quarter view'' trace their origins to the [[three-quarter profile]] in [[portrait]]ure and [[face perception|facial recognition]], which depicts a person's face that is partway between a frontal view and a side view.<ref>{{cite journal|title= Reassessing the 3/4 view effect in face recognition|journal=Cognition|date=February 2002|volume=83|issue=1|pages=31–48(18)|doi= 10.1016/S0010-0277(01)00164-0|pmid=11814485|last1= Liu|first1= C|s2cid=23998061}}</ref>
==Computer graphics==
===Axonometric and oblique projection===
{{See also|Isometric computer graphics}}
[[File:Lincity-ng.png|225px|thumb|''[[Lincity]]'' tiles 2D [[axonometric]] graphical elements to form a pseudo-3D game environment.]]
In [[axonometric projection]] and [[oblique projection]], two forms of [[parallel projection]], the viewpoint is rotated slightly to reveal other facets of the environment than what are visible in a [[top-down perspective]] or side view, thereby producing a three-dimensional effect. An object is "considered to be in an inclined position resulting in foreshortening of all three axes",<ref name="WPCleanerAuto1">{{cite web|url=http://www.merriam-webster.com/dictionary/axonometric%20projection|title=Axonometric Projection|publisher=[[Merriam-Webster]]|website=merriam-webster.com|access-date=19 March 2018|archive-date=19 September 2011|archive-url=https://web.archive.org/web/20110919224952/http://www.merriam-webster.com/dictionary/axonometric%20projection|url-status=dead}}</ref> and the image is a "representation on a single plane (as a drawing surface) of a three-dimensional object placed at an angle to the plane of projection."<ref name="WPCleanerAuto1" /> Lines perpendicular to the plane become points, lines parallel to the plane have true length, and lines inclined to the plane are foreshortened.
They are popular camera perspectives among [[2D computer graphics|2D]] video games, most commonly those released for [[History of video game consoles (fourth generation)|16-bit]] or earlier and [[Handheld video game|handheld consoles]], as well as in later [[strategy video game|strategy]] and [[role-playing video game]]s. The advantage of these perspectives is that they combine the visibility and mobility of a [[Top-down perspective|top-down game]] with the character recognizability of a [[Side-scrolling video game|side-scrolling game]]. Thus the player can be presented an overview of the game world in the ability to see it from above, more or less, and with additional details in artwork made possible by using an angle: Instead of showing a humanoid in top-down perspective, as a head and shoulders seen from above, the entire body can be drawn when using a slanted angle; turning a character around would reveal how it looks from the sides, the front and the back, while the top-down perspective will display the same head and shoulders regardless.
{{multiple image
| align     = left
| width     = 125
| image1    = Sprite anatomy 2d.svg
| image2    = Sprite anatomy 3d.svg
| footer    = Anatomy of an axonometric sprite. 2D [[Sprite (computer graphics)|sprite]] coordinates are on the left. 3D model coordinates are on the right.
}}
There are three main divisions of axonometric projection: ''isometric'' (equal measure), ''dimetric'' (symmetrical and unsymmetrical), and ''trimetric'' (single-view or only two sides). The most common of these drawing types in [[engineering drawing]] is isometric projection. This projection is tilted so that all three axes create equal angles at intervals of 120 degrees. The result is that all three axes are equally foreshortened. In video games, a form of dimetric projection with a 2:1 pixel ratio is more common due to the problems of anti-aliasing and square pixels found on most computer monitors.
In [[oblique projection]] typically all three axes are shown without foreshortening. All lines parallel to the axes are drawn to scale, and diagonals and curved lines are distorted. One tell-tale sign of oblique projection is that the face pointed toward the camera retains its right angles with respect to the image plane.{{clarify|date=January 2011}}
Two examples of oblique projection are ''[[Ultima VII: The Black Gate]]'' and ''[[Paperboy (video game)|Paperboy]]''. Examples of axonometric projection include ''[[SimCity 2000]]'', and the role-playing games ''[[Diablo (video game)|Diablo]]'' and ''[[Baldur's Gate (video game)|Baldur's Gate]]''.
===Billboarding===
In three-dimensional scenes, the term billboarding is applied to a technique in which objects are sometimes represented by two-dimensional images applied to a single polygon which is typically kept perpendicular to the line of sight. The name refers to the fact that objects are seen as if drawn on a [[billboard]]. This technique was commonly used in early 1990s video games when consoles did not have the hardware power to render fully 3D objects. This is also known as a backdrop. This can be used to good effect for a significant performance boost when the geometry is sufficiently distant that it can be seamlessly replaced with a 2D [[Sprite (computer graphics)|sprite]]. In games, this technique is most frequently applied to objects such as particles (smoke, sparks, rain) and low-detail vegetation. It has since become mainstream, and is found in many games such as ''[[Rome: Total War]]'', where it is exploited to simultaneously display thousands of individual soldiers on a battlefield. Early examples include early first-person shooters like ''[[Marathon Trilogy]]'', ''[[Wolfenstein 3D]]'', ''[[Doom (1993 video game)|Doom]]'', ''[[Hexen: Beyond Heretic|Hexen]]'' and ''[[Duke Nukem 3D]]'' as well as racing games like ''[[Carmageddon]]'' and ''[[Super Mario Kart]]'' and platformers like ''[[Super Mario 64]]''.
===Skyboxes and skydomes===
{{See also|Skybox (video games)}}
Skyboxes and skydomes are methods used to easily create a background to make a game [[level (video gaming)|level]] look bigger than it really is. If the level is enclosed in a cube, the sky, distant mountains, distant buildings, and other unreachable objects are rendered onto the cube's faces using a technique called [[cube mapping]], thus creating the illusion of distant three-dimensional surroundings.  A ''skydome'' employs the same concept but uses a [[sphere]] or [[Sphere|hemisphere]] instead of a cube.
As a viewer moves through a 3D scene, it is common for the skybox or skydome to remain stationary with respect to the viewer. This technique gives the skybox the illusion of being very far away since other objects in the scene appear to move, while the skybox does not. This imitates real life, where distant objects such as clouds, stars and even mountains appear to be stationary when the viewpoint is displaced by relatively small distances. Effectively, everything in a skybox will always appear to be infinitely distant from the viewer.  This consequence of skyboxes dictates that designers should be careful not to carelessly include images of discrete objects in the textures of a skybox since the viewer may be able to perceive the inconsistencies of those objects' sizes as the scene is traversed.
===Scaling along the Z axis===
In some games, sprites are scaled larger or smaller depending on its distance to the player, producing the illusion of motion along the Z (forward) axis. [[Sega]]'s 1986 video game ''[[Out Run]]'', which runs on the [[Sega OutRun]] [[arcade system board]], is a good example of this technique.
In ''Out Run'', the player drives a Ferrari into depth of the game window. The palms on the left and right side of the street are the same [[bitmap]], but have been scaled to different sizes, creating the illusion that some are closer than others. The angles of movement are "left and right" and "into the depth" (while still capable of doing so technically, this game did not allow making a U-turn or going into reverse, therefore moving "out of the depth", as this did not make sense to the high-speed game play and tense time limit). Notice the view is comparable to that which a driver would have in [[reality]] when driving a car. The position and size of any billboard is generated by a (complete 3D) perspective transformation as are the vertices of the poly-line representing the center of the street. Often the center of the street is stored as a spline and sampled in a way that on straight streets every sampling point corresponds to one scan-line on the screen. Hills and curves lead to multiple points on one line and one has to be chosen. Or one line is without any point and has to be interpolated lineary from the adjacent lines. Very memory intensive billboards are used in ''Out Run'' to draw corn-fields and water waves which are wider than the screen even at the largest viewing distance and also in [[Test Drive (1987 video game)|''Test Drive'']] to draw trees and cliffs.
''[[Drakkhen]]'' was notable for being among the first [[role-playing video game]]s to feature a three-dimensional playing field. However, it did not employ a conventional 3D game engine, instead emulating one using character-scaling algorithms. The player's party travels overland on a flat terrain made up of vectors, on which 2D objects are zoomed. ''Drakkhen'' features an animated day-night cycle, and the ability to wander freely about the game world, both rarities for a game of its era. This type of engine was later used in the game ''[[Eternam]]''.
Some mobile games that were released on the Java ME platform, such as the mobile version of [[Asphalt Urban GT|Asphalt: Urban GT]] and [[Driver: L.A. Undercover]], used this method for rendering the scenery. While the technique is similar to some of Sega's arcade games, such as [[Thunder Blade]] and [[Cool Riders]] and the 32-bit version of [[Road Rash (video game)#CD-based versions|Road Rash]], it uses polygons instead of sprite scaling for buildings and certain objects though it looks flat shaded. Later mobile games (mainly from Gameloft), such as [[Asphalt 4: Elite Racing]] and the mobile version of [[Iron Man 2 (video game)|Iron Man 2]], uses a mix of sprite scaling and texture mapping for some buildings and objects.
===Parallax scrolling===
{{Main|Parallax scrolling}}
[[File:Parallax_scroll.gif|thumb|225px|right|An example of [[parallax scrolling]]|alt=Three different image layers scrolling at different speeds]]
[[Parallax]]ing refers to when a collection of [[2D computer graphics|2D]] [[sprite (computer graphics)|sprite]]s or layers of sprites are made to move independently of each other and/or the background to create a sense of added depth.<ref name="Pile">{{cite book |last=Pile Jr |first=John |author-link=John Pile Jr |date=May 2013 |title=2D Graphics Programming for Games |url=http://www.crcpress.com/product/isbn/9781466501898 |location=New York, NY |publisher=CRC Press |isbn=978-1466501898 }}</ref>{{rp|103}} This depth cue is created by relative motion of layers. The technique grew out of the [[multiplane camera]] technique used in [[traditional animation]] since the 1940s.<ref name=art>{{cite web|title=The Art of Parallax Scrolling |url=http://mos.futurenet.com/pdf/net/NET165_tut_flash.pdf |first=Wyatt |last=Paul |date=August 2007 |access-date=2009-07-06 |url-status=dead |archive-url=https://web.archive.org/web/20091007223458/http://mos.futurenet.com/pdf/net/NET165_tut_flash.pdf |archive-date=2009-10-07 }}</ref> This type of graphical effect was first used in the 1982 [[arcade game]] ''[[Moon Patrol]]''.<ref>{{cite web|title=Chronology of the History of Video Games: Golden Age |url=http://www.thocp.net/software/games/golden_age.htm |first=Ted |last=Stahl |date=2006-07-26 |access-date=2009-11-21 |archive-url=https://web.archive.org/web/20091127183910/http://www.thocp.net/software/games/golden_age.htm |archive-date=27 November 2009 |url-status=live }}</ref>
Examples include the skies in ''[[Rise of the Triad]]'', the arcade version of ''[[Rygar]]'', ''[[Sonic the Hedgehog (1991 video game)|Sonic the Hedgehog]]'', ''[[Street Fighter II]]'', ''[[Shadow of the Beast (1989 video game)|Shadow of the Beast]]'' and ''[[Castlevania: Rondo of Blood#Castlevania: The Dracula X Chronicles|Dracula X Chronicles]]'', as well as ''[[Super Mario World]]''.
===Mode 7===
{{Main|Mode 7}}
[[Mode 7]], a display system effect that included rotation and scaling, allowed for a 3D effect while moving in any direction without any actual 3D models, and was used to simulate 3D graphics on the [[Super Nintendo Entertainment System|SNES]].
===Ray casting===
{{Main|Ray_casting#Ray_casting_in_early_computer_games|label 1=Raycasting in early computer games}}
[[File:Camera Rotation vs Shearing.gif|thumb|right|While tricks such as camera shearing (as seen on the right) are sometimes used to create an illusion of rotation, ray casting renderers cannot rotate said camera vertically<ref name="giantbomb_raycasting">{{cite web|url=https://www.giantbomb.com/ray-casting/3015-1517/|title=Ray Casting (Concept) - Giant Bomb|access-date=31 August 2021}}</ref> like true 3D renderers (left).]]
Ray casting is a [[First-person_(video_games)|first person]] pseudo-3D technique in which a ray for every vertical slice of the screen is sent from the position of the camera. These rays shoot out until they hit an object or wall, and that part of the wall is rendered in that vertical screen slice.<ref>{{cite web|url=http://lodev.org/cgtutor/raycasting.html|title=Raycasting|website=lodev.org|access-date=19 March 2018}}</ref> Due to the limited camera movement and internally 2D playing field, this is often considered 2.5D.<ref name="explanation_raycasting_2.5d">{{cite web|url=https://bytecode77.com/castenstein|access-date=31 August 2021|title=Castenstein - bytecode77}}</ref>
===Bump, normal and parallax mapping===
{{Main|Bump mapping|Normal mapping|Parallax mapping}}
'''Bump mapping''', '''normal mapping''' and '''parallax mapping''' are techniques applied to [[texture mapping|textures]] in [[3D rendering]] applications such as [[video game]]s to simulate bumps and wrinkles on the surface of an object without using more [[polygonal modeling|polygon]]s. To the end user, this means that textures such as stone walls will have more apparent depth and thus greater realism with less of an influence on the performance of the simulation.
'''Bump mapping''' is achieved by perturbing the [[surface normal]]s of an object and using a [[grayscale]] image and the perturbed normal during illumination calculations. The result is an apparently bumpy surface rather than a perfectly smooth surface although the surface of the underlying object is not actually changed. Bump mapping was introduced by Blinn in 1978.<ref name="Blinn">Blinn, James F. [http://dl.acm.org/citation.cfm?id=507101 "Simulation of Wrinkled Surfaces"], Computer Graphics, Vol. 12 (3), pp.&nbsp;286–292 SIGGRAPH-ACM (August 1978)</ref>
[[File:Bump-map-demo-full.png|thumb|right|300px|A sphere without [[bump mapping]] (left). The bump map to be applied to the sphere (middle). The sphere with the bump map applied (right).]]
In '''normal mapping''', the unit [[Vector (geometric)|vector]] from the shading point to the light source is [[dot product|dotted]] with the unit vector normal to that surface, and the dot product is the intensity of the light on that surface. Imagine a polygonal model of a sphere—you can only approximate the shape of the surface. By using a 3-channel bitmapped image textured across the model, more detailed normal vector information can be encoded. Each channel in the bitmap corresponds to a spatial dimension (''x'', ''y'' and ''z''). These spatial dimensions are relative to a constant coordinate system for object-space normal maps, or to a smoothly varying coordinate system (based on the derivatives of position with respect to texture coordinates) in the case of tangent-space normal maps. This adds much more detail to the surface of a model, especially in conjunction with advanced lighting techniques.
'''Parallax mapping''' (also called '''offset mapping''' or '''virtual displacement mapping''') is an enhancement of the bump mapping and normal mapping techniques implemented by displacing the texture coordinates at a point on the rendered polygon by a function of the view angle in tangent space (the angle relative to the surface normal) and the value of the [[height map]] at that point.  At steeper view-angles, the texture coordinates are displaced more, giving the illusion of depth due to [[parallax]] effects as the view changes.
== Film and animation techniques ==
The term is also used to describe an [[animation]] effect commonly used in music videos and, more frequently, title sequences. Brought to wide attention by the motion picture ''[[The Kid Stays in the Picture]]'', an adaptation of film producer [[Robert Evans (film producer)|Robert Evans]]'s memoir, it involves the layering and animating of two-dimensional pictures in three-dimensional space. Earlier examples of this technique include [[Liz Phair]]'s music video "Down" (directed by [[Rodney Ascher]]) and "A Special Tree" (directed by musician [[Giorgio Moroder]]).
On a larger scale, the 2018 movie ''[[In Saturn's Rings]]'' used over 7.5 million separate two-dimensional images, captured in space or by telescopes, which were composited and moved using multi-plane animation techniques.
==Graphic design==
The term also refers to an often-used effect in the design of [[Icon (computing)|icon]]s and [[graphical user interface]]s (GUIs), where a slight 3D illusion is created by the presence of a virtual light source to the left (or in some cases right) side, and above a person's [[computer display|computer monitor]]. The light source itself is always invisible, but its effects are seen in the lighter colors for the top and left side, simulating reflection, and the darker colours to the right and below of such objects, simulating shadow.
An advanced version of this technique can be found in some specialised graphic design software, such as Pixologic's [[ZBrush]]. The idea is that the program's canvas represents a normal 2D painting surface, but that the data structure that holds the pixel information is also able to store information with respect to a [[z-index]], as well material settings, [[specularity]], etc. Again, with this data it is thus possible to simulate lighting, shadows, and so forth.
==History==
The first video games that used pseudo-3D were primarily [[arcade game]]s, the earliest known examples dating back to the mid-1970s, when they began using [[microprocessor]]s. In 1975, [[Taito]] released ''[[Tomohiro Nishikado#Interceptor|Interceptor]]'',<ref name="Dreams">{{cite web|title=Tomohiro Nishikado's biography at his company's web site |publisher=Dreams, Inc. |archive-url=https://web.archive.org/web/20090401041713/http://www.dreams-game.com/profile/president.html |archive-date=2009-04-01 |url=http://www.dreams-game.com/profile/president.html |access-date=2011-03-27 |url-status=dead }}</ref> an early [[first-person shooter]] and [[Combat flight simulation game|combat flight simulator]] that involved piloting a [[Fighter aircraft|jet fighter]], using an eight-way [[joystick]] to aim with a crosshair and shoot at enemy aircraft that move in formations of two and increase/decrease in size depending on their distance to the player.<ref name=Interceptor>{{KLOV game|8195|Interceptor}}</ref> In 1976, [[Sega]] released ''[[Fonz (arcade)|Moto-Cross]]'', an early black-and-white [[motorbike]] [[racing video game]], based on the [[motocross]] competition, that was most notable for introducing an early three-dimensional [[Third-person (video games)|third-person]] perspective.<ref name=Moto-Cross>{{KLOV game|12812|Moto-Cross}}</ref> Later that year, [[Gremlin Industries|Sega-Gremlin]] re-branded the game as ''[[Fonz (arcade)|Fonz]]'', as a tie-in for the popular [[sitcom]] ''[[Happy Days]]''.<ref name=Fonz>{{KLOV game|id=12812|name=Fonz}}</ref> Both versions of the game displayed a constantly changing forward-scrolling road and the player's bike in a third-person perspective where objects nearer to the player are larger than those nearer to the horizon, and the aim was to steer the vehicle across the road, racing against the clock, while avoiding any on-coming motorcycles or driving off the road.<ref name=Moto-Cross/><ref name=Fonz/> That same year also saw the release of two arcade games that extended the car [[driving]] subgenre into three dimensions with a [[First person (video games)|first-person]] perspective: Sega's ''Road Race'', which displayed a constantly changing forward-scrolling S-shaped road with two obstacle race cars moving along the road that the player must avoid crashing while racing against the clock,<ref name=Road-Race>{{KLOV game|12733|Road Race}}</ref> and [[Atari]]'s ''[[Night Driver (arcade game)|Night Driver]]'', which presented a series of posts by the edge of the road though there was no view of the road or the player's car. Games using [[vector graphics]] had an advantage in creating pseudo-3D effects. 1979's ''Speed Freak'' recreated the perspective of ''Night Driver'' in greater detail.
In 1979, [[Nintendo]] debuted ''[[Radar Scope]]'', a [[shoot 'em up]] that introduced a three-dimensional third-person perspective to the genre, imitated years later by [[Shooter game|shooters]] such as [[Konami]]'s ''[[Juno First]]'' and [[Activision]]'s ''[[Beamrider]]''.<ref>{{cite web|url=http://www.1up.com/do/feature?pager.offset=1&cId=3181467|archive-url=https://web.archive.org/web/20121017222352/http://www.1up.com/do/feature?pager.offset=1&cId=3181467|url-status=dead|archive-date=17 October 2012|title=Where Were They Then: The First Games of Nintendo, Konami, and More from 1UP.com|date=17 October 2012|access-date=19 March 2018}}</ref> In 1980, Atari's ''[[Battlezone (1980 video game)|Battlezone]]'' was a breakthrough for pseudo-3D gaming, recreating a 3D perspective with unprecedented realism, though the gameplay was still planar. It was followed up that same year by ''[[Red Baron (1980 video game)|Red Baron]]'', which used scaling vector images to create a forward scrolling [[rail shooter]].
[[Sega]]'s arcade shooter ''Space Tactics'', released in 1980, allowed players to take aim using crosshairs and shoot lasers into the screen at enemies coming towards them, creating an early 3D effect.<ref>{{KLOV game|id=9683|name=Space Tactics}}</ref> It was followed by other arcade shooters with a first-person perspective during the early 1980s, including [[Taito]]'s 1981 release ''[[List of Taito games|Space Seeker]]'',<ref>{{KLOV game|id=9682|name=Space Seeker}}</ref> and Sega's ''[[Star Trek (arcade game)|Star Trek]]'' in 1982.<ref>{{KLOV game|9770|Star Trek}}</ref> Sega's ''[[SubRoc-3D]]'' in 1982 also featured a first-person perspective and introduced the use of [[List of stereoscopic video games|stereoscopic 3-D]] through a special eyepiece.<ref>{{KLOV game|9856|SubRoc-3D}}</ref> Sega's ''[[Astron Belt]]'' in 1983 was the first [[laserdisc video game]], using [[full-motion video]] to display the graphics from a first-person perspective.<ref>{{cite web|url=http://www.allgame.com/game.php?id=9550|title=Astron Belt - Overview - allgame|archive-url=https://web.archive.org/web/20141114095114/http://www.allgame.com/game.php?id=9550|archive-date=2014-11-14}}</ref> [[Third-person shooter|Third-person]] rail shooters were also released in arcades at the time, including Sega's ''[[Tac/Scan]]'' in 1982,<ref>{{KLOV game|id=10007|name=Tac/Scan}}</ref> [[Nippon Electric Company|Nippon]]'s ''Ambush'' in 1983,<ref>{{KLOV game|6878|Ambush}}</ref> [[Nihon Bussan|Nichibutsu]]'s ''[[Nihon Bussan#Action role-playing|Tube Panic]]'' in 1983,<ref>{{cite web|url=http://www.allgame.com/game.php?id=32709|title=Tube Panic - Overview - allgame|archive-url=https://web.archive.org/web/20141115105644/http://www.allgame.com/game.php?id=32709|archive-date=2014-11-15}}</ref> and Sega's 1982 release ''[[Buck Rogers: Planet of Zoom]]'',<ref>{{KLOV game|7227|Buck Rogers – Planet Of Zoom}}</ref> notable for its fast pseudo-3D scaling and detailed sprites.<ref name=IGN-Sega/>
In 1981, Sega's ''[[Turbo (video game)|Turbo]]'' was the first racing game to use [[Sprite (computer graphics)|sprite]] scaling with full-colour graphics.<ref name=IGN-Sega>{{cite web|url=http://www.ign.com/articles/2009/04/21/ign-presents-the-history-of-sega|title=IGN Presents the History of SEGA|first=Travis|last=Fahs|date=21 April 2009|website=ign.com|access-date=19 March 2018}}</ref> ''[[Pole Position]]'' by [[Namco]] is one of the first racing games to use the trailing camera effect that is now so familiar {{Citation needed|date=September 2023}}.  In this particular example, the effect was produced by linescroll—the practice of scrolling each line independently in order to warp an image.  In this case, the warping would simulate curves and steering.  To make the road appear to move towards the player, per-line color changes were used, though many console versions opted for [[palette animation]] instead.
''[[Zaxxon]]'', a shooter introduced by Sega in 1982, was the first [[Isometric graphics in video games|game to use isometric]] [[axonometric projection]], from which its name is derived. Though Zaxxon's playing field is semantically 3D, the game has many constraints which classify it as 2.5D: a fixed point of view, scene composition from sprites, and movements such as bullet shots restricted to straight lines along the axes. It was also one of the first video games to display shadows.<ref name=Perron>Bernard Perron & Mark J. P. Wolf (2008), ''Video game theory reader two'', [https://books.google.com/books?id=oe0zNalKkTgC&pg=PA158 p. 158], [[Taylor & Francis]], {{ISBN|0-415-96282-X}}</ref> The following year, Sega released the first pseudo-3D [[Isometric adventure game|isometric platformer]], ''[[Congo Bongo]]''.<ref>{{KLOV game|id=7384|name=Congo Bongo}}</ref> Another early pseudo-3D [[platform game]] released that year was [[Konami]]'s ''[[Antarctic Adventure]]'', where the player controls a penguin in a forward-scrolling third-person perspective while having to jump over pits and obstacles.<ref name=KLOV-Antarctic>{{KLOV game|6890|Antarctic Adventure}}</ref><ref name=allgame-Antarctic>{{cite web|url=http://www.allgame.com/game.php?id=19267|title=Antarctic Adventure - Overview - allgame|archive-url=https://web.archive.org/web/20141114184713/http://www.allgame.com/game.php?id=19267|archive-date=2014-11-14}}</ref><ref name=Moby-Antarctic>{{MobyGames|id=/msx/antarctic-adventure|name=Antarctic Adventure}}</ref> It was one of the earliest pseudo-3D games available on a computer, released for the [[MSX]] in 1983.<ref name=Moby-Antarctic/> That same year, [[Irem]]'s ''[[Moon Patrol]]'' was a [[Side-scrolling video game|side-scrolling]] [[Run and gun (video game)|run & gun]] platform-shooter that introduced the use of layered [[parallax scrolling]] to give a pseudo-3D effect.<ref name="parallax">{{cite web|url=http://www.gamesradar.com/f/gamings-most-important-evolutions/a-20101008102331322035/p-3 |archive-url=https://archive.today/20110615221817/http://www.gamesradar.com/f/gamings-most-important-evolutions/a-20101008102331322035/p-3 |archive-date=2011-06-15 |title=Gaming's most important evolutions |publisher=GamesRadar |url-status=dead }}</ref> In 1985, ''[[Space Harrier]]'' introduced Sega's "[[Sega Super Scaler|Super Scaler]]" technology that allowed pseudo-3D [[Sprite (computer graphics)#Move to 3D|sprite-scaling]] at high [[frame rate]]s,<ref name="autogenerated1">{{cite web|url=http://www.ign.com/articles/2009/04/21/ign-presents-the-history-of-sega?page=3|title=IGN Presents the History of SEGA|date=21 April 2009|website=ign.com|access-date=19 March 2018}}</ref> with the ability to scale 32,000 [[Sprite (computer graphics)|sprites]] and fill a moving landscape with them.<ref>Bernard Perron & Mark J. P. Wolf (2008), ''Video game theory reader two'', p. 157, [[Taylor & Francis]], {{ISBN|0-415-96282-X}}</ref>
The first original home [[console game]] to use pseudo-3D, and also the first to use multiple camera angles mirrored on television sports broadcasts, was ''[[Intellivision World Series Baseball]]'' (1983) by [[Don Daglow]] and [[Eddie Dombrower]], published by [[Mattel]]. Its television sports style of display was later adopted by 3D [[sports game]]s and is now used by virtually all major team sports titles. In 1984, Sega ported several pseudo-3D arcade games to the [[Sega SG-1000]] console, including a smooth conversion of the third-person pseudo-3D rail shooter ''Buck Rogers: Planet of Zoom''.<ref name="autogenerated1"/>
By 1989, 2.5D representations were surfaces drawn with depth cues and a part of graphic libraries like GINO.<ref name="Raper">Raper, Jonathan. "The 3-dimensional geoscientific mapping and modeling system: a conceptual design." In Three dimensional applications in Geographic Information Systems, edited by Jonathan F. Raper, 11–19. Philadelphia: Taylor and Francis Inc., 19.</ref> 2.5D was also used in terrain modeling with software packages such as ISM from Dynamic Graphics, GEOPAK from Uniras and the Intergraph DTM system.<ref name="Raper "/> 2.5D surface techniques gained popularity within the geography community because of its ability to visualize the normal thickness to area ratio used in many geographic models; this ratio was very small and reflected the thinness of the object in relation to its width, which made it the object realistic in a specific plane.<ref name="Raper "/> These representations were axiomatic in that the entire subsurface domain was not used or the entire domain could not be reconstructed; therefore, it used only a surface and a surface is one aspect not the full 3D identity.<ref name="Raper "/>
The specific term "two-and-a-half-D" was used as early as 1994 by Warren Spector in an interview in the North American premiere issue of [[PC Gamer]] magazine. At the time, the term was understood to refer specifically to first-person shooters like [[Wolfenstein 3D]] and [[Doom (1993 video game)|Doom]], to distinguish them from [[System Shock]]'s "true" 3D engine.
With the advent of consoles and [[computer system]]s that were able to handle several thousand [[polygon]]s (the most basic element of ''[[3D computer graphics]]'') per second and the usage of 3D specialized [[graphics processing unit]]s, pseudo-3D became obsolete. But even today, there are computer systems in production, such as cellphones, which are often not powerful enough to display ''true'' 3D graphics, and therefore use pseudo-3D for that purpose. Many games from the 1980s' ''pseudo-3D arcade era'' and ''16-bit console era'' are ported to these systems, giving the manufacturers the possibility to earn revenues from games that are several decades old.
[[File:Geabios alps.gif|thumb|Fly through the [[Trenta (valley)|Trenta Valley]]]]
The resurgence of 2.5D or visual analysis, in natural and earth science, has increased the role of computer systems in the creation of spatial information in mapping.<ref name="MacEachren "/> GVIS has made real the search for unknowns, real-time interaction with spatial data, and control over map display and has paid particular attention to three-dimensional representations.<ref name="MacEachren "/> Efforts in GVIS have attempted to expand higher dimensions and make them more visible; most efforts have focused on "tricking" vision into seeing three dimensions in a 2D plane.<ref name="MacEachren "/> Much like 2.5D displays where the surface of a three-dimensional object is represented but locations within the solid are distorted or not accessible.<ref name="MacEachren "/>
==Technical aspects and generalizations==
{{Unreferenced section|date=March 2023}}
The reason for using pseudo-3D instead of "real" 3D computer graphics is that the system that has to simulate a 3D-looking graphic is not powerful enough to handle the calculation-intensive routines of 3D computer graphics, yet is capable of using tricks of modifying 2D graphics like [[bitmap]]s. One of these tricks is to stretch a bitmap more and more, therefore making it larger with each step, as to give the effect of an object coming closer and closer towards the player.
Even simple shading and size of an image could be considered pseudo-3D, as shading makes it look more realistic. If the light in a 2D game were 2D, it would only be visible on the outline, and because outlines are often dark, they would not be very clearly visible. However, any visible shading would indicate the usage of pseudo-3D lighting and that the image uses pseudo-3D graphics. Changing the size of an image can cause the image to appear to be moving closer or further away, which could be considered simulating a third dimension.
Dimensions are the variables of the data and can be mapped to specific locations in space; 2D data can be given 3D volume by adding a value to the ''x'', ''y'', or ''z'' plane. "Assigning height to 2D regions of a topographic map" associating every 2D location with a height/elevation value creates a 2.5D projection; this is not considered a "true 3D representation", however is used like 3D visual representation to "simplify visual processing of imagery and the resulting spatial cognition".
==See also==
*[[3D computer graphics]]
*[[Bas-relief]]
*[[Cel-shaded animation]]
*[[Flash animation]]
*[[Head-coupled perspective]]
*[[Isometric graphics in video games]]
*[[Limited animation]]
*[[List of stereoscopic video games]]
*[[Live2D]]
*[[Ray casting]]
*[[Trompe-l'œil]]
*[[Vector graphics]]
==References==
{{reflist|colwidth=30em}}
<!-- 1. MacEachren, Alan. "GVIS Facilitating Visual Thinking."  In How Maps Work: Representation, Visualization, and Design, 355-458. New York: The Guilford Press, 1995.
2. Raper, Jonathan. "The 3-dimensional geoscientific mapping and modeling system: a conceptual design." In Three dimensional applications in Geographic Information Systems, edited by Jonathan F. Raper, 11–19. Philadelphia: Taylor and Francis Inc., 1989.
3. Uddin, Saleh. "Conventions and Construction of Paralines." In Axonometric and Oblique Drawing: A 3-D Construction, Rendering, and Design Guide, 1–14. New York: McGraw-Hill, 1997.
4. Watt, R.J. and B.J. Rogers. "Human Vision and Cognitive Science." In Cognitive Psychology Research Directions in Cognitive Science: European Perspectives Vol. 1, edited by Alan Baddeley and Niels Ole Bernsen, 10–12. East Sussex: Lawrence Erlbaum Associates, 1989. 5. Wood, Jo, Sabine Kirschenbauer, Jurgen Dollner, Adriano Lopes, and Lars Bodum. "Using 3D in Visualization." In Exploring Geovisualization, edited by Jason Dykes, Alan M. MacEachren, and Menno-Jan Kraak, 295–312. Oxford: Elsevier Ltd, 2005. -->
{{Computer graphics}}
[[Category:Video game development]]
[[Category:Video game graphics]]
[[Category:Video games with 2.5D graphics]]
[[Category:Dimension]]